1. Field of the Invention
The invention relates to a method of estimating a mounting angle error, and a turning device.
2. Description of Related Art
As a technique of this type, Japanese Patent Application Publication No. 2010-271918 (JP 2010-271918 A) describes attitude control over a two-wheeled inverted pendulum robot that uses an angular velocity sensor (gyro sensor) and an acceleration sensor. Because an output value of the angular velocity sensor degrades over time, a correction value of the angular velocity sensor is obtained by, for example, supporting the two-wheeled inverted pendulum robot with a special jig and then the two-wheeled inverted pendulum robot is rotated at a set rotation speed from a rearmost inclined position to a frontmost inclined position in JP 2010-271918 A.
Incidentally, if there is an error in a mounting angle of a pitch axis angular velocity sensor for executing inverted pendulum control over a two-wheeled inverted pendulum vehicle with respect to a reference axis of a body, when the two-wheeled inverted pendulum vehicle turns (turns around its yaw axis), a turning component of the error may be detected by the pitch axis angular velocity sensor and, therefore, an inverted pendulum reference angle may gradually deviate. As a result, the two-wheeled inverted pendulum vehicle is inverted in a state where the vehicle is inclined forward or rearward when the vehicle stops turning. This makes an occupant experience discomfort.
In addition, similarly, if there is an error of a mounting angle of a roll axis angular velocity sensor with respect to the reference axis of the body, when the vehicle turns, forward or rearward inclination of the two-wheeled inverted pendulum vehicle sways to vary. This similarly makes the occupant experience discomfort.
Against such a problem, in an existing art, a measure is taken for setting errors of the mounting angles of the respective angular velocity sensors with respect to the reference axis of the body to zero as much as possible. In this measure, there is a problem in terms of reduction in the size and weight of the body of the two-wheel inverted pendulum vehicle because a high-accuracy frame for ensuring various accuracies, such as a mounting accuracy between each angular velocity sensor and an inclination sensor that serves as a horizontal reference axis and a mounting accuracy between a sensor block, which includes the angular velocity sensors and the inclination sensor, and the body of the two-wheeled inverted pendulum vehicle, is required, for example.
Further description will be made on the above-described problem due to a mounting error. It is assumed that, for example, a mounting error of the pitch axis angular velocity sensor, which is used to execute inverted pendulum control over the two-wheeled inverted pendulum vehicle, with respect to a turning plane (that is, a yaw turning plane) is β0 [rad] around the roll axis and the vehicle turns at an angular velocity γ dot. In this case, γ dot×sin(β0) [rad/sec] is output from the pitch axis angular velocity sensor as an error. Specifically, when the mounting error β0 of the pitch axis angular velocity sensor with respect to the turning axis is 0.5 [deg], rotation around the pitch axis is recognized through a turn of 360 [deg] as if the vehicle rotates an accumulation of about 3 [deg] around the pitch axis.
Such an error of pitch angular velocity through a turn occurs in a relatively low frequency band, so it is conceivable that an error is cancelled by a high-pass filter or using deadband (neutral zone). However, for example, when a turn direction is changed rightward or leftward minutely, the high-pass filter is not useful at all, so there may be an accumulation of errors in computation process of obtaining a pitch angle by integrating a pitch angular velocity, and the pitch angle may deviate unlimitedly.